It is well known to provide integrated circuit packages in which integrated circuits (dies), principally composed of semiconductor material, are located within resin bodies. Electrical contacts of the integrated circuit are electrically in contact with corresponding electrical conductors that protrude out of the resin body.
In one type of package, the integrated circuits are located on a die pad portion of a lead frame with the electric contacts facing away from the lead frame, and wires are formed between the electric contacts and respective lead fingers of the lead frame. The resin is applied to encase the integrated circuits and the wires in the resin body, leaving a portion of the lead frames protruding from the resin body. The lead fingers are then cut to separate them from the remainder of the lead frame, and thus singulate the packages.
An alternative type of integrated circuit is called a “flip-chip,” which is positioned on (and normally adhered to) a substrate with the electrical contacts facing the substrate, and in electrical contact with corresponding electric contacts provided in the substrate. The electric contacts on the substrate are typically electrically connected to electrically conductive paths formed through the material of the substrate. The flip-chip is typically encased in a resin body which secures it to the substrate to form a package.
There is pressure to improve integrated circuit packages to increase the number of input/output connections (I/Os), reduce the package footprint, reduce the package thickness and improve the thermal management (that is, reduce the risk of the integrated circuit overheating).
Various proposals have been made to do this, typically proposing that a plurality of dies are packaged into a single package. For example, it is known to provide a plurality of dies inside a single package stacked one above the other with an adhesive paste between them. It is further known to provide two dies placed side-by-side (e.g., on a lead frame) within a single resin body.
One disadvantage with providing a stacked die package assembly is that the thickness of the package is increased. Additionally, there are reliability concerns due to the reduced possibilities for heat dissipation, which in turn lead to an increased risk of overheating.
Conversely, providing the dies side-by-side means that the footprint of the package is increased.
A separate development in the field of packaging is to employ flexible substrates, that is substrates consisting of an element of flexible material onto which an integrated circuit can be mounted, and carrying electrically conductive paths for electrical connection to electric contacts of the integrated circuit, e.g., by the wire-bonding or flip-chip techniques. The preferred base material for flexible substrates is polyimide, although other materials (such as polyester, fluorocarbon films, aramid papers, and composites) are also known. These are quite different from the materials used to make conventional substrates. There are numerous advantages in providing flexible substrates to help in the miniaturization of electronic products. For example, if the substrate is flexible, the product is less likely to be sensitive to variations in temperature, since the substrate can absorb heat shrinkage or expansion of components of the product.